The present invention relates generally to electronic communications.
Networks provide communication sessions between clients and servers where, generally speaking, clients request information provided by servers. Some networks provide a high degree of security, so that messages passing between clients and servers are protected from unauthorized interception, reading, or tampering. Other networks, particularly more public networks such as the Internet, do not themselves necessarily protect from unauthorized reception of messages. Communications sessions and messages can be encoded to lend a degree of protection.
In addition, servers on public networks are vulnerable to discovery by unauthorized users, who can try to "hack" into such servers to obtain otherwise confidential information. Fire walls have been developed which help protect against unwanted intruders. Users, after logging onto a public network server, can be identified by any of a number of schemes (e.g., passwords), and then be transferred to other servers to access more sensitive information.
Network clients, especially Internet clients, often access the Internet through routers, or proxies. For example, a network client may be a particular user on a local area network (LAN). The network client may not have a valid Internet address, but may have a valid TCP/IP address (certain ranges of IP addresses are called "private" or "invalid" addresses and can be used within an organization's LAN but do not work over the Internet). Nonetheless, the network client can send and receive messages via the Internet by having those messages communicated through a device which does have a valid Internet address. For example, e-mail clients can access e-mails sent and received via the Internet from their e-mail server attached to their LAN, which in turn can attach to an Internet server which has a valid IP address and is attached to the Internet. The Internet has protocols (e.g., IMAP) for constructing and addressing e-mail messages so that e-mail clients properly receive their e-mail.
Computer users may also desire to access information that exists on particular computers attached to a LAN. One method for doing so requires a direct connection between the computer user and the LAN resource. For example, an employee can directly call (via a modem) a LAN computer that has a dedicated telephone port. A number of remote access applications provide for such connections. Such remote access applications allow the employee to remotely control and view the operations of a work computer, e.g., the employee's desktop computer, or a special computer having access to common LAN files at work.
However, if the employee wishes to have more flexible access to a LAN resource, for example, by using an existing remote access application but over the Internet instead of through a dedicated phone connection, there are some difficulties. Apart from securing the communication session itself (by, e.g., encryption), typical LAN resources do not have their own, Internet-acceptable, IP addresses. For example, an employee's LAN computer might have a LAN address of "10.0.0.3." Should message packets be sent to or from that LAN computer with that address, typical Internet routers will drop them as having improper IP addresses.
One might try using some form of network address translation (NAT), which operates at the IP layer, to translate improper LAN addresses to some other arbitrary proper IP address, and back again. However, such a method would require a translation of each message packet's address, a recalculation of the checksum of the packet, and then a rewriting of the packet for delivery.
Even if a LAN resource has a proper IP address, it might not be desirable to make it known. For example, a firm might want several clients to have access to subsets of information applicable to each client separately, but not give that client access to other clients' information. The firm might put the information on a common Internet server, behind a firewall, and allocate client access by Uniform Resource Locator (URL): e.g., one client accesses information at http:// . . . //client A, another client at http:// . . . //client B. However, it can be difficult to develop a sufficiently complex set of different URLs for a variety of clients that is not also susceptible to someone figuring out its organization and accessing protected data.
LAN administrators may not want to give a LAN resource its own IP address, but also may not want to give others (for example, clients) network address translation information, since that information can include sensitive specifics about the LAN configuration. Also, administrators may not want any information about the location of a particular resource sent through the Internet, to lessen the chance others might locate the resource without authorization and try to break into it.